Reporting bias in 'mentally ill' killers

I have noticed a recent mass-media trend in light of the latest mass shooting in Connecticut, USA, that killed 27—20 of whom were children. I have noticed in most instances, that perpetrators were Caucasian males who were diagnosed by the mass media as "mentally ill".

Without undermining the severity or prevalence of mental and neurological disorders, it often makes me wonder "what if" the perpetrator were of another ethnicity or religious background, would the diagnosis be the same?

Recent perpetrators of mass human carnage, including the movie theatre shooting in Colorado in July or the Sikh temple shooting near Massachusetts in August, all carried the same mass-media rhetoric.

I am not specifically talking about the fact that if you perpetrate such an act, you have to be mentally ill (some may doubt this) but rather the "who" perpetrates it; would they also be deemed so? It then begs the question that if the perpetrator's background were Middle Eastern or of the Islamic faith, would they now be considered mentally ill or a terrorist?

The reason being that there are crimes of similar brutality that take place all the time by ethnic minorities in the inner cities of developed countries to the ghettoes, slums and villages of developing countries—yet the perpetrators of these crimes are said to have "no regard for the law or human life". It is almost as if the mass media diagnoses first then gathers information to "support" the symptoms rather than use the symptoms to diagnose afterwards.

One example that sheds light on this observation was the sniper shootings that took place ten years ago in Washington DC, Maryland and Virginia where co-conspirator John Allen Muhhumad, a Muslim and former sniper in the US Army, was branded a terrorist, or of that nature, in some mass media outlets, with no allusion to possible mental illness, yet it is not uncommon for veterans to return from wars socially and psychologically withdrawn, suicidal, mentally ill or unstable. I noticed a careful reference to his military background only in highlighting his expertise with firearms and target accuracy.

The omnipresent and homologous news frames used by the mass media when reporting such tragedies should provoke discussions such as these more often.